Nozzles have long been used to atomize fluids, such as liquids, gases and liquid-solid slurries, to provide fine sprays. One particular application of atomizers that has received considerable attention is in fuel combustion. It is now well known that atomizers that deliver a fine spray of discrete minute droplets improve combustion efficiency.
Thus, considerable work has been done to develop atomizer nozzles that enhance fuel burning efficiency in power plant boilers. It is generally accepted that the finer the fuel spray pattern, the more complete and effective the combustion will be. However, other limitations such as nozzle vibration, tube temperatures, opacity and nitrogen oxide (NO.sub.x) emissions must be considered when designing fuel atomizers.
In about 1989 Todd Combustion, Shelton, Conn. developed an atomizer nozzle that improved the combustion efficiency and to some extent reduced NO.sub.x emission. The prior art Todd Combustion atomizer was developed for application in a now conventional furnace windbox.
The Todd atomizer is characterized as a Multi-Jet Single Fluid Atomizer. Structurally the atomizer has a cup-shaped internal whirling chamber into which fuel under pressure is delivered through an array of passages or slots that are arranged tangentially to the whirling chamber. An array of perimeter holes each of which are the same radial distance from the center of the whirling chamber provide passage of the fuel from the whirling chamber to the furnace combustion chamber.
In addition, prior art atomizers with a plurality of perimeter holes such as disclosed in U.S. Pat. No. 5,143,297 also exist.
Although the prior art designs reduced NO.sub.x emissions over previous designs, the level of NO.sub.x emission was still not satisfactory and opacity was higher than desirable. As a result considerable research was conducted to obtain an aerator nozzle capable of reducing opacity to minimal levels.